When collecting resources during the kingdom phase, and drawing cards during the quest phase, do you base the number of resources and cards taken on the overall power in the corresponding zone (factoring in modifiers that give more power, but don't actually display a specifically red power icon), or merely on the actual red power icons in the zone?

Power enhancers surely count.

For example: Shrine to Taal gives 1 unit extra power for each development in it's zone. This extra power counts towards the gaining of recources/cards.

You include modifiers, not just the red icons, but also hammer symbols in the card text. However, you only count hammers that are active during your Kingdom phase. For example, if a card says "...gets +P +P while attacking" then you do not count those 2 power when counting up resources.

Thanks for clarifying, guys.